Conference Programme

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Overview
Session
F-03: Transparent conductors and smart coating
Time:
Tuesday, 20/Jun/2017:
10:30am - 12:00pm

Session Chair: Thomas Unold, Helmholtz-Zentrum Berlin
Session Chair: Jin Hyeok Kim, Chonnam National University
Location: Rm 336

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Presentations
10:30am - 11:00am
Keynote

Amorphous CdO-Ga2O3 Transparent Conductors for Flexible Electronics

Kin Man YU

City University of Hong Kong, Hong Kong S.A.R. (China)

Transparent conductors (TCs) are an essential component in a number of semiconductor technologies including portable electronics, flat-panel displays, low-e windows, solar cells. Appropriately doped wide gap metal oxides (e.g. Al doped ZnO or Tin doped In2O3) are typically used as TCs for most applications. For flexible electronics (including flexible organic solar cells), deposition of these TCs must be carried out at temperatures lower than the deformation temperature of flexible polymer substrates. Low temperature deposited, wide gap ionic amorphous oxides (IAOs) such as InGaZnO (IGZO) have been suggested as potential materials for flexible electronics because of their good conductivity (~1000-10000 S/cm) with relatively high mobility (>10 cm2/Vs). Our previous work has demonstrated that cadmium oxide (CdO) deposited at elevated temperatures of 200-500oC has high mobility values of ~200-500 cm2/Vs with an electron concentration of 1020-1021 cm-3 and therefore can be exploited as a potential candidate for such application. In this work CdO-Ga2O3 alloy films (Cd1-xGaxO1+δ) over the whole composition range (x=0 to 1) were synthesized at room temperature by radio frequency magnetron sputtering on glass and plastic substrates. We found that unlike other IAOs which have a limited bandgap range of ~3.2-3.5 eV, the band gap of Cd1-xGaxO1+δ alloys can be tuned in a wide range from 2.2 to 4.8 eV. As the Ga content increases to x>0.3 the alloy becomes entirely amorphous. Within the amorphous alloy rage, materials with resistivity <10-3 Ω-cm and mobility >10 cm2/Vs can be achieved on both glass and plastic (PEN) substrates. These results suggest that amorphous Cd1-xGaxO1+δ alloy films can be used as TCs on flexible solar cells as well as gate electrodes with a wide bandgap tunabilty for transparent/flexible devices. The electronic structures and optical properties of these alloys will also be discussed in this talk.


11:00am - 11:30am
Invited

Copper-Based P-Type Transparent Conductive Oxide Layers as Potential Electrode for Photovoltaic Solar Cells

Alain BILLARD1, Hui SUN1, Mohammad ARAB POUR YAZDI1, Frédéric SANCHETTE2

1University of Technology of Belfort-Montbéliard, France; 2University of Technology of Troyes, France

P-type TCO’s suffer of a lack of conductivity that should be overcame to allow applications in various domains such as in photovoltaics. Cuprous oxide Cu2O is known as a potential candidate despite its optoelectronic performance remains insufficient. Among the technics susceptible to permit the deposition of p-type layers for photovoltaic applications, Physical Vapour Deposition processes present several advantages such as a low deposition temperature or the possibility to tune the oxygen content in a single phased supersaturated solid solution which in turns modifies the opto-electronic performances of the coating.

In this presentation we will first describe the properties of Cu2O coatings deposited by using different PVD processes which yield more or less high energy impinging species (pulsed-DC, HiPIMS, ion assisted magnetron sputtering …).

Hence, we will describe the deposition and the associated opto-electronic properties of copper-based delafossite structure CuCrO2 coatings deposited by co-sputtering, also using different processes in relation with the energy of the coating building species. Their enrichment by Mg substituted to Cr will also be discussed as a function of the opto-electronic performances of the films characterized by their Figure of Merit.

Finally, the influence of intercalation of a noble metal layer (e.g. silver or gold) will be presented for Cu2O coatings as well as for CuCrO2(:Mg) regarding with their opto-electronic performance.


11:30am - 11:45am
Oral

Thermochromic Properties of VO2 Films obtained by Air-Annealing of Sputter-Deposited VN Films Doped with a Third Element

David PILLOUD1, Fabien CAPON1, Aurélien DIDELOT1,2, David MERCS2, Patrice MISKA1, Jean-François PIERSON1

1Institut Jean Lamour, Université de Lorraine, France; 2Viessmann Faulquemont, France

Due to its reversible metal-insulator transition (MIT) at Tc = 68 °C, VO2 is an extensively studied material. In thin film form, VO2 is promising for numerous applications, including solar energy management. However, such a transition temperature is not suitable for all technological purposes, e.g. Tc has to be lowered to ambient temperature for smart windows, and conversely, should increase for thermochromic solar panels. Doping VO2 films is often considered to overcome this problem. Up-to-date, among the various methods to deposit VO2 films, reactive sputtering is mainly used but requires a stringent control of the stoichiometry due to the numerous phases belonging to the binary V-O system. A recent approach developed by Xu [1] and called “sputtering-oxidation-coupling method” consists in oxidizing metallic vanadium films obtained by sputter deposition. The work presented here aims to investigate another source material to obtain pure thermochromic VO2 films after oxidation: vanadium nitride and to study the doping effect of such films.

Doped-VN films were reactively sputtered and annealed in air during short times (less than 7 minutes). Oxidized films were characterized by X-ray diffraction, scanning electron microscopy, spectroscopies (Raman, UV-vis and FTIR), 4-point probe and IR-thermography. Our results showed that doping has significant effect on the oxidation resistance of VN films and on the thermochromic properties of the resulting VO2 phase. Finally, the functional properties of VO2 films formed after VN oxidation are compared with those of films synthesized after V oxidation.

Reference:

[1] X. Xu, X. He, G. Wang, X. Yuan, X. Liu, H. Huang, S. Yao, H. Xing, X. Chen, J. Chu, Appl. Surf. Sci. 257 (2011) 8824.


11:45am - 12:00pm
Oral

Water Wettability of Metal Oxide Surfaces and the Effect of Oxygen Vacancy

Siddhartha GHOSH1, Meenakshi ANNAMALAI1, Abhijeet PATRA1, Saurav PRAKASH1,3, T VENKATESAN1,2,4

1NUS Nanoscience and Nanotechnology Initiative (NUSNNI)-NanoCore, National University of Singapore, Singapore; 2Department of Physics, Faculty of Science, National University of Singapore, Singapore; 3NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore; 4Department of Materials Science and Engineering, National University of Singapore, Singapore

Understanding the structural, physical and chemical properties of the surface and interfaces of different metal-oxides and their possible applications in photo-catalysis and biology is a very important emerging research field. Motivated in this direction, we would discuss the understanding of how different fluids, particularly water, interact with oxide surfaces. We have studied the water contact angle of 3d transition metal oxide thin films of SrTiO3, and of 4f rare-earth oxide thin films of Lu2O3. These metal oxides were grown using pulsed laser deposition and they are atomically flat and with known orientation and explicitly characterized for their structure and composition. Further study was done on the effects of oxygen vacancies on the water contact angle of the 3d and 4f oxides. For 3d SrTiO3 oxide with oxygen vacancies, we have observed an increase in hydroxylation with consequent increase of wettability which is in line with the previous reports whereas an interesting opposite trend was seen in the case of rareearth Lu2O3 oxide. Density functional theory simulations of water interaction on the above mentioned systems have also been presented to further substantiate our experimental findings.


12:00pm - 12:15pm
Oral

Growth and Characterization of Cuprous Oxide (Cu2O ) Nanorods by Reactive Ion Beam Sputter Deposition (IBSD) Method.

Assamen Ayalew EJIGU, Laing-Chiun CHAO

National Taiwan University of Science and Technology, Taiwan

In recent semiconductor and nanotechnology, quality material synthesis, proper characterizations, and productions are the big challenges. As cuprous oxide (Cu2O) is a promising semiconductor material for photovoltaic (PV) and other optoelectronic applications, this study was aimed at to grow and characterize high quality Cu2O nanorods for the improvement of the efficiencies of thin film solar cells and other potential applications.

In this study, well-structured cuprous oxide (Cu2O) nanorods were successfully fabricated using IBSD method in which the Cu2O samples were grown on silicon substrates.

The characterization of the Cu2O nanorods (NRs) were done in comparison with Cu2O thin film (TF) deposited with the same method but with different Ar:O2 flow rates. With Ar:O2 ratio of 9:1 single phase pure polycrystalline Cu2O NRs with diameter of ~500 nm and length of ~4.5 µm were grow. Increasing the oxygen flow rates, pure single phase polycrystalline Cu2O TF was found at Ar:O2 ratio of 6:1. The field emission electron microscope (FE-SEM) measurements showed that both samples have smooth morphologies. X-ray diffraction and Rama scattering measurements reveals the presence of single phase Cu2O in both samples.

Raman characterization shows that the Cu2O NRs sample has pronounced Raman band intensities, higher numbers of Raman bands than the Cu2O TF.

The temperature PL spectra measurements, showed that the defect luminescent band centered at 720 nm is the dominant one for the Cu2O NRs and the 640 nm band was the only PL band observed from the Cu2O TF. The difference in optical and structural properties of the samples comes from the oxygen flow rate change in the process window.

Finally, the novel morphologies, excellent structural and optical properties seen exhibits the grown Cu2O NRs sample has enough quality to be used in further research of the nano/micro structured semiconductor materials.



 
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